Grid glow tube circuits



y 1937. L. E. SWEDLUND 2,088,494

' GRID GLOW TUBE CIRCUITS Filed Aug. 24, 1935 Fly. 1.

Load

M'mM I Pate/717a] WITNESSES: INVENTOR LloydBYE. Swazi/and Patented July 27, 1937 UNITED STATES GRID GLOW TUBE CIRCUITS Lloyd E. Swedlund,

Montclair, N. 1., assignor to Westinghouse Electric & Manufacturing Com- D y, East Pittsburgh, Pennsylvania Pa., a corporation of Application August 24, 1935, Serial No. 37,759

8 Claims.

My invention relates to electric discharge apparatus and it has particular relation to apparatus in which power supplied to a load is controlled by the operation of a hot cathode discharge device having a control electrode.

In the apparatus to which my invention relates, the discharge device is of the type having an anode, a cathode that is to be directly heated, and a control electrode. The anode and cathode are preferably, though not necessarily, surrounded by an atmosphere of a gas such as neon or argon or a vapor such as mercury. The cathode consists generally of a spiral properly coated with an emissive substance and it is heated by alternating current.

To control the output of the discharge device, control potentials are impressed between the control electrode and the cathode. In accordance with the teachings of the prior art of which I am aware, the return conductor for the control electrode is connected to a point (preferably the center tap) of the secondary of the transformer whereby the cathode is energized. The effect of the control potential in producing changes in the condition of the discharge device depends on the magnitude of potential impressed between the most positive point of the cathode and the control electrode. When the cathode is connected to an intermediate tap of the oathode supply secondary, a potential corresponding to the difference of potential between the intermediate tap and the most positive point of the cathode is superimposed on the control potential.

The superimposed potential is in magnitude equal approximately to half the magnitude of the potential of the cathode-supply source and its frequency is twice the frequency of the source. Where the control potential available is comparatively small and must be applied precisely, the pulsations superimposed by the cathode heating source produce difficulties. Further difficulties are produced in situations where the discharge device is to be energized at a predetermined frequency. In the latter case, the pulsations of twice the frequency of the cathode-heating source produce difiiculties.

It is accordingly an object of my invention to provide electric discharge apparatus of the type incorporating a hot cathode electric discharge device, the cathode of which is energized from an alternating current source, in which the effect of the alternating current source on the control potential shall be compensated.

Another object of my invention is to provide for apparatus incorporating an electric discharge device having 2. directly heated cathode in which the cathode is supplied from an alternating current source, a circuit by the operation of which the effect, on the control potential of the discharge device, produced by the cathode heating source shall be suppressed.

Moreconcisely stated, it is an object of my invention to provide electrical discharge apparatus, incorporating an electric discharge device having a control electrode and a directly heated cathode, in which the discharge device shall be precisely and accurately controlled in spite of the fact that the cathode is heated from an alterhating current source.

According to one embodiment of my invention, 1 provide a control circuit incorporating a contrivance whereby the conductor that couples the control electrode to the cathode is always maintained at the potential of the most positive point of the cathode. This object may be accomplished by connecting a plurality of rectifying elements across the source in such manner that one conducts for one half cycle and the other for the half cycle of opposite polarity. The return lead from the control circuit is connected to the junction point of the rectifiers.

In accordance with a modification of my invention, the pulsating potential introduced is suppressed by impressing in the control circuit a compensating potential of opposite polarity and of the same magnitude as the pulsating potential.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments, when read in connection with the accompanying drawing, in which Figure 1 is a diagrammatic view showing an embodiment of my invention.

Fig. 2 is a diagrammatic view showing the essential features of a modification of the apparatus shown in Fig. 1.

Fig. 3 is a diagrammatic view showing the essential features of another modification of the apparatus shown in Fig. 1.

Fig. 4 is a diagrammatic view showing a modification of my invention, and

Fig. 5 is a diagrammatic view showing another modification of my invention.

The apparatus shown in Fig. 1 comprises an electric discharge device I having an anode 3, a cathode 5 and a control electrode 1. The elec terminal.

trodes 3, 5 and l are enclosed in an envelope in which an atmosphere of a gas such as neon or argon at a pressure of the order of from several microns to several millimeters is present in a vapor l'l'lGdlUIl'l, such as that provided by globule of mercury disposed in the envelope. While my invention is principally applied to discharge devices of this type, it may also be applied to hot cathode discharge devices of the high vacuum type and where the principles of my invention are essentially involved in apparatus of the latter type, the preferred arrangement discussed above should in no way be taken as limiting the scope of my invention.

The cathode 5 of the electric discharge device I is customarily a metallic helix suitably coated for emissive purposes. To heat the cathode, an alternating source of potential 9 is provided. The source supplies the cathode 5 through a transformer H, the secondary iii of which has a plurality of terminal taps it and ll, and an intermediate tap [9. Between the intermediate tap IQ of the secondary l3 and the anode 3 of the discharge device i, a load El is connected through a source 23 of suitable character. Between the terminal taps l5 and ll of the secondary l3, a network comprising a plurality of oppositely connected rectifiers 25 and 2? is connected. While the rectifiers 25 and ill may be of any general type, I prefer to use copper-oxide elements known to the trade as Rector; rectifiers. Between the junction point 29 of the rectifiers 5 and 2'! and the intermediate it of the secondary I3, an impedance 35, preferably a resistor of high magnitude is connected. The rectifiers 25 and 2'? and the resistor 31 are so connected to the secondary i3 that when one terminal, say the left hand terminal, or the secondary is positive, current flows through one of the rectifiers 25 and the resistor 3!, and the point 23 is at the potential of this terminal; and when the other terminal of the secondary is positive, current flows through the rectifier 22'! and the resistor 34, and the point 29 is at the potential of the latter The point 29 is therefore always at the potential of the most positive point of the secondary l3.

Potential between the control electrode the cathode 5 is provided in the usual well known manner. In the apparatus shown in Fig. 1, the control potential is supplied through a voltage divider 33 which is, in turn, in circuit with the control electrode 7. The return conductor 35 from the control electrode I is connected to the junction point 25 of the rec i and tifiers 25 and 27.

To understand the operation of the apparatus, assume that the left hand terminal of the oathode secondary i3 is at a certain instant positive with respect to the right hand terminal. a case, the left hand terminal of the cathode 5 is the most positive point of the cathode. same time, the left hand rectifier 25 1s conductive of the rectifiers is at the same potential as the cathode 5.

situation the most positive emissive portion of the cathode 5 is at a lower potential than the most positive terminal of the source at any given in- To compensate for the discrepancy, the apparatus shown in Fig. 2 is utilized.

In apparatus of this type, the return conductor 35 from the control circuit is connected not directly to the junction point 29 of the rectifiers 25 and 27 but to a point on the resistor 31 which is of the proper potential to compensate for the drop in the conductors.

On other occasions, it may happen that the drop across the network incorporating one or the other of the rectifiers 25 and 27 is of appreciable magnitude. To take care of the difiiculty arising in this connection, the apparatus shown in Fig, 3 is provided. Here a cathode supply secondary 37 is utilized which is provided with a plu rality of pairs of terminal taps 39 and 41 and 43 and 45. The rectifiers 25 and 2'! are connected between the taps 39 and ll between which the potential difference is greatest while the cathode 5 is supplied by the potential output between the taps 43 and between which the potential difference is smallest. The taps 39, ll, t3 and 45 may be so adjusted that the drop in potential across the rectifiers 25 and 21 is compensated. It is apparent, of course, that if the rectifiers have different conductive impedances, the outer terminal taps and ii may be adjusted properly to take care of the difference.

In the modification fier network; utilized in the apparatus shown in Figs. 1 to 3 is replaced by a Graetz connected and operation of the apparatus is otherwise not changed.

In the apparatus shown in Fig. 5, the elTect of the pulsating potential introduced by the cathode heating source is suppressed by providing an additional pulsating potential of the same frequency and magnitude but of opposite polarity. In apparatus of this type, the source (not shown) whereby the cathode 5 is energized also supplies the load 2i through the discharge,

device l. The load 2! is supplied through a t9 connected in such manner from the source.

Across the positive terminals 5] and 53 of the rectifier it a voltage divider E5 is connected. The intermediate tap 119 of the secondary I3 is connected to an intermediate point 571 of the voltage divider 55. The return conductor 35 from the control circuit is connected to another point 59. The latter point is so related to the first mentioned point 51 introduced by the cathode supply are suppressed.

That the compensating pulsations need be rectified will be seen from a consideration of the circuit. Since the control circuit is connected essentially to the electrical center of the cathode supply source, the potential superimposed in the control circuit by the cathode supply source is half the amplitude of the cathode supply potential.

as to be energized necessary compensation.

Although I have shown and described certain My invention, therefore, is

prior art and by claims.

I claim as my invention:

1. In combination, an electric discharge device having a cathode and another electrode, a source of periodic potential for heating said cathode, a plurality of asymmetrically conducting elements, means for connecting said elements across said source in such manner that one is conductive only to current of one polarity while the other is conductive only to current of the opposite polarity and a connection for said other electrode connected to the junction point of said elements.

2. In combination, an electric discharge device having a cathode and another electrode, a source of alternating potential for heating said cathode, a plurality of asymmetrically conducting elements, means for connecting said elements across said source in such manner that one is conductive only to current of one polarity while the other is conductive only to current of the opposite polarity and a connection for said other electrode connected to the junction point of said elements.

3. In combination, an electric discharge device having a cathode and another electrode, a source of periodic potential for heating said cathode, means for connecting said source to said cathode, the potential of all points displaced from its electrical center of said cathode when so connected varying in accordance with the periodicity of said source, whereby the most positive point of said cathode shifts along the cathode in accordance with the periodicity of said source, means in circuit with said other electrode for impressing an external difference of potential between said cathode and said other electrode, the last said means including a conductor leading to said cathode and means for shifting the potential of said conductor in accordance with the periodicity of said source so that it is always at the potential of the most positive point of the cathode.

4. In combination, an electric discharge device having a cathode and another electrode, a source of periodic potential for heating said cathode, a plurality of asymmetrically conducting elements, means for connecting said elements across said source in such manner that one is conductive only to current of one polarity while the other is conductive only to current of the opposite polarity, impedance means connected'between the junction point of said elements and an intermediate point of said source and a connection for said other electrode connected to the junction point of said elements.

5. In combination, an electric discharge device the spirit of the appended having a cathode and another electrode, a source of alternating current potential for heating said cathode, a plurality of asymmetrically conducting elements, means for connecting said elements across said source in such manner that one is conductive only to current of one polarity while the other is conductive only to current of the opposite polarity, impedance means connected between the junction point of said elements and an intermediate point of said source, and a connection for said other electrode connected to the junction point of said elements.

6. In combination, an electric discharge device having a cathode, an anode and a control electrode, a source of periodic potential for heating said cathode, a pluarity of asymmetrically conducting elements, means for connecting said elements across said source in such manner that one is conductive only to current of one polarity while the other is conductive only to current of the opposite polarity, and a connection for said control electrode connected to the junction point of said elements.

'7. In combination, an electric discharge device having a cathode, an anode and a control electrode, a source of alternating potential for heating said cathode, means for connecting said source to said cathode, all points displaced from the neutral point of said cathode when so con nected varying in potential in accordance with the frequency of said source, whereby the point of maximum potential of said cathode shifts back and forth along said cathode with a frequency corresponding to the frequency of said source, a circuit connected between said control electrode and a point of said source, said circuit functioning to apply control potentials between said control electrode and said cathode and including a current path leading to said source, a terminal of said current path being connected to a point of said source between which and the most positive point of said cathode a difference of potential exists and means included in said current path for interposing an additional potential between said terminal of said current path and the portion thereof leading to the remainder of said circuit, that is, of a magnitude equal and of a polarity opposite to said difference of potential between said point of said source and said most positive point of said cathode.

8. Apparatus according to claim 4:, characterized by that the point of the source to which the terminal is connected is substantially at its electrical center and the additional potential is composed of rectified half waves derived from the source.

LLOYD SWEDLUND 

